The present invention relates to a telephone having an automatic audio response function wherein an addressee can answer a telephone call without picking up a handset thereof.
A telephone which can be used hands-free is becoming widespread. Such a telephone is convenient when the addressee has her hands full.
In a conventional telephone with the automatic audio response function, in order to connect the line to the telephone when the telephone bell rings, a hands-free button is operated. In another type, the line is automatically connected with the telephone by speaking to the telephone.
FIG. 7 is a block diagram showing an example of the conventional main telephone of the latter type.
Referring to FIG. 7, when a ringer 1 detects a bell signal coming through a telephone line, a CPU 2 applies a control signal to a bell signal generator 3, which in response applies a ring signal to a speaker 7 through a speech circuit 4, hands-free circuit 5, and an amplifier 6. Thus the bell tone is sounded through the speaker 7. The bell signal is usually fed at a cycle of the ON of one second with a pause of two seconds therebetween. When a microphone 11 picks up a vocal response during the pause of the bell within a predetermined time, the vocal sound is applied to the CPU 2 through an amplifier 12. The CPU 2 accordingly feeds a closing signal to a line closing circuit 9 comprising a pair of transistors Tr1 and Tr2, rendering the transistors conductive. Hence a voice signal from the other end of the line is transmitted to the speaker 7 through a rectifier 8, line closing circuit 9, speech circuit 4, hands-free circuit 5 and the amplifier 6. Namely, the voice of the caller can be heard from the speaker without operating any button on the telephone. The voice of the addressee picked up by the microphone 11 is transmitted to the hands-free circuit 5, amplified at the speech circuit 4 and further transmitted to the addresser.
After the conversation is over, when the addresser puts the handset of the addresser's telephone on the cradle, a busy tone signal is fed from the addresser's telephone to the addressee's telephone through the telephone line. The busy tone signal is applied to a busy tone detector 10 which detects the signal. As a result, the CPU 2 applies an open signal to the line closing circuit 9 to disconnect the line.
The call can also be made to a cordless telephone shown in FIG. 8 through the main telephone of FIG. 7. The bell signal fed to the main telephone is applied to the cordless telephone through an RF modulator 13 and an antenna 14 of the main telephone.
Referring to FIG. 8, an antenna 20 receives the bell signal and applies it to a CPU 22 through an RF modulator 21. The CPU 22 accordingly applies a ring demand signal to a speaker 24 through an amplifier 23, thereby ringing a bell. When a voice is picked up by a microphone 26 during the pause of the bell within a predetermined time, the CPU 22 applies a response signal to the CPU 2 of the main telephone through the RF modulator 21, antennas 20 and 14 and the RF modulator 13. The CPU 2 thus applies the closing signal to the line closing circuit 9 as described above, thereby making a connection. Thus the hands-free transmission becomes possible.
When the addresser puts down the handset, the busy tone signal is fed to the main telephone and detected by the busy tone detector 10. The CPU 2 accordingly transmits a signal demanding the termination of the transmission to the cordless telephone, and automatically cuts off the line.
Such a conventional telephone with the automatic audio response function often interprets intermittent noises in a noisy surroundings as a vocal response to the bell, thereby erroneously connecting the line. In order to prevent the erroneous operation, the applicant of the present invention has proposed in Japanese Patent Application No. 7-101099, a telephone wherein a threshold for determining the vocal response and inducing the connection of the line is changed in accordance with the conditions of the ambient sound field of the telephone.
More particularly, as shown in FIG. 9a, the bell signal is usually transmitted at a cycle of one second with an interval of two seconds. As shown in FIG. 9b, the bell is sounded alternately at 791 Hz and 631 Hz at a cycle of 48 ms each in order that sufficient sound pressure is maintained and that a mellow sound quality of the bell is obtained.
On the other hand, the energy of the human voice such as "Yes|" responding to the bell is concentrated in a range under 800 Hz regardless of the sex. Namely, the frequencies of the bell and of the voice overlap with each other so that the voice cannot be detected while the telephone is ringing. Thus the detection of the response is suspended while the telephone is ringing, and carried out only during the pause. Namely, the hands-free operation is executed when the level of the voice input through the microphone exceeds a predetermined threshold within a predetermined time and determined as a response, and during the pause of the bell as shown in FIG. 10. Hence, the addressee intentionally has to speak out while the telephone is silent, which is quite troublesome.